Filament wound structure for use as a torque drive

ABSTRACT

A filament wound fiber reinforced resin matrix composite structure. The structure is particularly adapted for use as a torque drive diaphragm in a rotary wing aircraft hub. The structure comprises a substantially flat diaphragm and a rim. The diaphragm has a central hole therethrough for receiving a shaft and the rim has an inward turning flange for attachment. The diaphragm has an attachment means surrounding the central hole. An alternative embodiment of the structure is a hollow disc having first and second substantially flat diaphragm sides with a rim. The sides have concentric central holes therethrough and attachment means surround the holes. The structure comprises a resin matrix, fibers wound substantially tangentially to the central hole with sufficient tension in a multiple circuit pattern to form the structure, and fibers wound with sufficient tension in an essentially circumferential manner to reinforce the rim of the structure. The structure is cured by molding with sufficient heat and temperature in a controlled cure cycle. The structure does not exhibit &#34;oil-canning&#34; in that the flat diaphragm or diaphragm sides do not displace from the substantially flat uniplanar mode when subjected to varying temperatures. The spring characteristics of the structure when constrained as a torque drive remain approximately linear and buckling and snap-through are eliminated during operation.

This is a division of application Ser. No. 734,982 filed on May 16,1985, now U.S. Pat. No. 4,666,753.

TECHNICAL FIELD

The field of art to which this invention relates is fiber reinforcedresin matrix composites, more particularly to composite diaphragmstructures.

BACKGROUND ART

In order to transfer energy from a turbine engine, a conventionalcombustion engine, an electric motor or any power generating apparatusto a machine to power that machine, it is typically necessary to jointhe power generating apparatus to the machine with some sort of couplingmeans. These apparatuses typically transmit power through an angularlyrotating shaft and this power output is typically referred to as torque.The power coupling means is a critical piece of equipment since itsfailure will typically result in the de-energization of the machine.

When a power generating apparatus having a high horsepower output (e.g.a 1,000 H.P. electric motor) is coupled to a machine having a highangular velocity shaft (e.g., a centrifugal pump), it is critical thatthe shafts of the devices are aligned as closely as possible.Misalignment will result in a number of problems including adversevibration levels, premature bearing failure, structural damage,overheating, excessive noise, and high wear rate and failure rate of thecoupling. Although it is theoretically possible to perfectly align theshafts of the power generating apparatus and the machine, there arepractical limitations including measurement equipment, equipmentlocation, adverse environmental factors, differential rates of thermalexpansion during operation, etc. In addition, a the design may require aspecified amount of articulation. There are couplings in the prior artwhich permit slight shaft misalignment for high torque, high speedapplications, however, the amount of misalignment is typically about1/2° or less and these couplings are typically of metal construction andvery heavy. The primary limitation of the power couplings of the priorart is that the materials of construction do not permit high torque andhigh angular velocity with large shaft misalignment, up to about 10°,across a broad temperature spectrum. Such a power coupling must act as atorque transmitting or driving means, and, it must also act as a flexureto permit elastic deformation to compensate for the misalignment.

The power coupling means is particularly crucial in rotary wing aircraftor helicopters. The power coupling means used in helicopters to transfertorque from the power shaft to the helicopter blades is typicallyreferred to as a rotary hub. The rotary hubs of the prior art werecomplex, metal mechanisms. The disadvantages of these metal rotary hubswere several including weight fatigue failure, very high maintenance andcost.

There is a constant search in this art to replace metal aircraft partswith lightweight, high strength, fatigue resistant composite components.An example of a helicopter gimbal rotor hub utilizing compositematerials is contained in U.S. Pat. No. 4,323,332 which is incorporatedby reference.

The elimination of conventional roller bearings and ball bearings in therotor hub of a helicopter is accomplished in a composite gimbal rotorhub by utilizing composite materials in the blade and hub which arecapable of bending and rotating to accommodate blade pitch, flap andlead-lag motion. The rotor hub restrains the blades against centrifugalforce and transmits lifting force from the blades to the shaft andairframe of the helicopter. Since the rotary hub should tilt about thecentral axis of the shaft in a composite hub design, it is necessary toprovide a tiltable means for transferring torque from the shaft to therotor blades. The torque drive structure must be rigid enough totransmit torque directly from the shaft to the helicopter blades but yetmust be sufficiently flexible and bendable to act as a spring and tiltup approximately 10° from horizontal while transmitting the torque load.The typical power output to a hub assembly is in excess of 1,000 H.P.Conventional materials do not have the properties required tosimultaneously perform the torque driving function and spring functionwithout structural failure.

Accordingly, what is needed in this art is a flexible composite torquetransfer means and a method of manufacturing such a torque transfermeans that overcomes the problems of the prior art.

DISCLOSURE OF THE INVENTION

A fiber reinforced resin matrix composite structure, particularlyadapted for use as a torque drive diaphragm in a rotary wing aircrafthub, is disclosed. The structure comprises a circular diaphragm having arim, said rim having an inward turning flange for attachment, and acentral hole therethrough for receiving a shaft. The structure comprisesa resin matrix, reinforcing fibers wound substantially tangentially tothe central hole in a multiple circuit pattern to form a diaphragmsection of the structure and a rim having an inward turning flange, andreinforcing fibers wound in an essentially circumferential manner toreinforce the rim section of the structure and balance the overallthermal characteristics of the structure. The structure is wound withsufficient fiber tension and cured by molding with sufficient heat andpressure. The diaphragm section of the structure remains essentiallyuniplanar when subjected to stresses induced by temperature changes.

Another aspect of this invention is a method of forming a fiberreinforced resin matrix composite structure, particularly adapted foruse as a torque drive diaphragm in rotary wing aircraft hub, comprisingwinding fiber impregnated with thermosetting resin at sufficient fibertension on a mandrel substantially tangentailly to a central hole in amultiple circuit pattern to form a diaphragm having a rim and an inwardturning flange, winding reinforcing fibers impregnated with resin atsufficient fiber tension in an essentially circumferential manner toreinforce the rim section of the structure, wherein the reinforcingfibers are optionally interleaved with the tangential fibers to form thestructure. The structure is then cured by molding at sufficient heat andpressure. The diaphragm section of the structure remains essentiallyuniplanar when subjected to stresses induced by temperature changes.

Another aspect of this invention is a fiber reinforced resin matrixcomposite structure, particularly adapted for use as a flexible torquedrive coupling. The structure comprises a hollow disc having a firstsubstantially flat diaphragm side and a second substantially flatdiaphragm side, each diaphragm side having a central hole therethroughconcentric with the central axis of the disc for receiving a shaft. Eachdiaphragm side also has a means for attachment centrally located aroundthe central hole. The disc has a peripheral rim joining the diaphragmsides. The structure comprises a resin matrix, fiber, wound withsufficient tension substantially tangentially to the central holes in amultiple circuit pattern to form the disc and fiber wound withsufficient tension in an essentially circumferential manner to reinforcethe peripheral rim of the structure and balance the overall thermalcharacteristics of the structure. The structure is cured by molding withsufficient heat and pressure such that the diaphragm sections remainessentially uniplanar when subjected to stresses induced by temperaturechanges.

Yet another aspect of this invention is a method of forming a fiberreinforced resin matrix composite structure, particularly adapted foruse as a flexible torque drive coupling. The method comprises windingfiber impregnated with resin on a mandrel substantially tangentially toa central hole with sufficient fiber tension using a multiple circuitpattern to form a disc having a first substantially flat diaphragm sideand a second substantially flat diaphragm side said disc having aperipheral rim joining said diaphragm sides, wherein each diaphragm sidehas a central hole therethrough concentric with the central axis of thedisc for receiving a shaft and a means for attachement centrally locatedaround the central hole, winding reinforcing fibers impregnated withresin with sufficient tension in an essentially circumferential mannerto reinforce the rim section of the structure, wherein the reinforcingfibers are optionally interleaved with the tangential fibers to form thestructure, the structure is then cured by molding at sufficient heat andpressure such that the diaphragm sides of the disc remain essentiallyuniplanar when subjected to stresses induced by temperature changes.

The combined effects of the circumferential rim properties and fiberpre-tension result in a diaphragm part with substantially improvedthermal properties, thereby eliminating oil-canning tendencies.

The foregoing and other features and advantages of the present inventionwill become more apparent from the following description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a preferred embodiment of the fiber wound torquetransmitting structure of the present invention.

FIG. 2a is a plan view of a partial schematic of a typical compositehelicopter rotor hub assembly incorporating the torque drive structureof the present invention.

FIG. 2b is a side view of a cross section of the rotor hub assembly.

FIG. 3 is a partial cross-section of the fiber wound torque transmittingstructure of the present invention.

FIG. 4 illustrates a typical winding pattern for a fiber wound torquetransmission structure according to the present invention.

FIG. 5 illustrates an optional 3 circuit winding pattern for rimreinforcement.

FIG. 6 illustrates an optional 4 circuit winding pattern for rimreinforcement.

FIG. 7 illustrates optional reinforcing patterns for the structure ofthe present invention.

FIG. 8 illustrates a coupling using the torque drive structure of thepresent invention.

FIG. 9 is a sectional view of a coupling using the torque drivestructure of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The fibers which are used to manufacture the torque transmissionstructures of the present invention will comprise fibers known in theart for manufacturing composite structures. Some examples of thesefibers include polyaramid fiber, graphite fiber, glass fiber, andcombinations thereof. The fibers will typically have a tensile strengthof about 70,000 to about 550,000 psi, preferably about 400,000 psi. Aparticularly preferred synthetic fiber in the practice of this inventionis Kevlar 29® brand polyaramid fiber manufactured by DuPont Company,Wilmington, Del. Kevlar 29® brand polyaramid fiber has a tensilestrength of about 400,000 psi and a tensile modulus of 9,000,000 psi.The fiber is typically purchased in the form of commercially availableprefabricated roving or tape. Tape will typically comprise about 8rovings. The tape used to wind the structures of the present inventionis typically about 0.5 inch to about 12 inches in width, more typicallyabout 0.5 inch to about 6 inches and preferably about 0.5 inch. Thepreferred width of tape used in winding a structure will depend upon andvary with the size of the structure. The thickness of the tape istypically about 0.050 inch to about 0.002 inch, more typically about0.012 inch to about 0.006 inch and preferably about 0.006 inch.

It is preferred to use polyaramid tape which has been preimpregnatedwith resin, although nonimpregnated tape can be used and the resinsubsequently impregnated therein during processing.

A structure of the present invention comprising Kevlar® polyaramidfibers and resin matrix will have a unidirectional tensile modulus ofabout 10,000,000 psi to about 12,000,000 psi at room temperature. Thefiber to resin ratio of a structure of the present invention formed frompolyaramid fibers and resin matrix will be about 55% to about 65% byvolume.

Graphite fibers may also be used in the practice of this invention.Graphite fibers generally have a tensile strength of about 400,000 psito about 600,000 psi. The diameter of typically used graphite fibersranges from about 0.00025" to about 0.00030". Graphite fibers, likepolyaramid fibers, are typically used in the form of roving or tape.Roving typically comprises about 12,000 fibers. It is preferred to useroving or graphite fibers which are preimpregnated with thermosettingresin, although it is possible to purchase nonimpregnated fibers and toimpregnate the fibers with resin matrix prior to winding operations. Apreferred graphite fiber is Celion® brand graphite fibers manufacturedby Celanese Chemical Company, New York, N.Y. Additional examples ofgraphite fibers which can be used in the practice of this invention areT-300® Brand graphite fibers available from Union Carbide Corporation,New York, N.Y. and AS-4® brand graphite fibers available from Hercules,Inc., Wilmington, Del. The graphite fiber roving or tape usually has athickness of about 0.012", although thicknesses such as 0.006" are alsoavailable. The cured graphite and resin matrix composite should containabout 50% to about 65% by volume of fibers. A structure of the presentinvention comprising graphite fibers and resin matrix will have aunidirectional tensile modulus of about 18,000,000 to about 25,000,000psi at room temperature.

Glass fiber material may also be used in the practice of the presentinvention. The preferred glass fiber is an S-type or E-type which iscommercially available preimpregnated with epoxy resin ornonimpregnated. Preimpregnated glass fibers are available in the form offiber roving or tape having widths of about 0.1" to about 1.0" andthicknesses of between 0.06" and about 0.0125". The optional thicknessand width is related to the size and loading of the structure. Thestructure of the present invention when formed from a glass fiber andresin matrix will have about 45% to about 60% by volume fiber content. Astructure of the present invention comprising glass fibers and resinmatrix will have a undirectional tensile modulus of about 5,000,000 psito about 7,000,000 psi at room temperature.

The resin matrix will comprise a thermosetting or thermoplastic resinwhich is capable of bonding to the synthetic fiber. The resin may beorganic or inorganic. Typical of the resins which can be used in thepractice of this invention are epoxy, polyester, polyimid, and otherhigh temperature crosslinked polymer structures. A particularlypreferred resin is American Cyanamid epoxy resin no. 1806, purchasedfrom American Cyanamid Co., Wayne, N.J. This resin is a high straincapacity resin. Examples of commercially available resins include epoxyresin no. 35101-B manufactured by Hercules, Inc., Wilmington, Del.;epoxy resin no. 5143 and epoxy resin no. 1806 manufactured by AmericanCyanamid Co., Wayne, N.J.; polyimide resin no. E-7178 manufactured byU.S. Polyimide Co., and resin no. E-746 manufactured by U.S. ProlamCorporation. The tape or roving, as previously mentioned, can be usedeither pre-impregnated with resin or the tape or roving can beimpregnated with resin during the winding process by methods known inthe art such as by passing the tape through a reservoir of resinsolution prior to winding. Another method is a resin transfer moldingprocess wherein resin is injected into the mold and thereby incorporatedinto the fiber structure. It is preferred in the practice of thisinvention to use tape or roving which has been pre-impregnated withresin.

The torque drive structures of the present invention are manufactured byusing a mandrel and a commercially available automated filament windingapparatus. The mandrel comprises a silicone rubber outer coating and aninner supporting ring consisting of detachable metal sections orsegments. The mandrel is placed in a fixture on the winding apparatusand a preprogramed winding pattern is used to wrap the mandrel with thefiber tape or roving to produce a fiber layer or ply of sufficientthickness having sufficient fiber orientation. Although most windingpatterns which produce a symmetric and tailored layer of fiber havingessentially radial orientation may be used in the practice of thisinvention, it is preferred to use an eleven circuit winding pattern.FIG. 4 illustrates a basic eleven circuit winding pattern for the torquedrive structure. The angle between each tape 55 is approximately33.2308°. After the eleven circuits are completed the pattern isautomatically shifted approximately 5.5385° until the pattern iscompleted and a structural layer of fiber has been wound onto mandrel50. The tape or roving 55 is wound on mandrel 50 essentially orsubstantially tangentially to the central hole in the structure.

Composite structures which comprise filament wound resin impregnatedresin-fiber matrices appear to have the strength for use as torquedrives or couplings for high power, high angular velocity,shaft-misalignment or shaft articultion, and tilting applications.Typically a torque drive for a rotor hub or a power coupling willcomprise at least one hub area, at least one substantially flatdiaphragm area, a rim area and an attachment means. The compositestructures are typically radially wound with resin impregnated fiber ona mandrel so that the fiber orientation is substantially radial at theperiphery while tangential to a central hole therein. A problem with acomposite wound structure having a flat diaphragm section is that thediaphragm section tends to "oil-can" or displace from the desireduniplanar mode. This problem is attributable to a differential thermalexpansion coefficient between the synthetic fiber and the resin.

Specifically, unidirectional composites have two principal coefficientsof thermal expansion, the longitudinal coefficient of expansion α_(L) inthe direction in which the fibers run, and the transverse coefficient ofexpansion α_(t) in the direction transverse to the fibers. For acomposite material the longitudinal coefficient α_(L) is usually muchsmaller than the tranverse coefficient α_(t) because the fibers, whichusually have a smaller coefficient than that for the resin matrix, tendto impose a mechanical restraint on the resin matrix material.

With regard to the filament wound diaphragm torque drive, the mix offiber angles in the wound composite part changes significantly from thecenter region to the outer radius of the diaphragm section. The centerregion has a mix of high fiber angles which changes to predominantlyradial orientation at the rim. Therefore, in the central portion thermalexpansion is dominated by the fiber (having a low coefficient ofexpansion), while in the rim area, the resin matrix is dominant (havinga high coefficient of expansion), particularly in the tangentialdirection.

As a result, when the part undergoes a temperature change of any kind,the central portion of the diaphragm expands or contracts at a muchlower rate than the outer radius or rim section. Such a composite fiberwound structure when cooled down to ambient temperature after a typicalhigh temperature cure will shrink in uneven proportions. In addition,the structure, while in use, will be subject to temperature changes ofits environment which may amplify the problem. The outer radius or rimarea shrinks at a much greater rate than the central portion of thediaphragm as a result of the fiber angle variation. As a result, thecentral portion of the diaphragm part is placed in compression with aresulting tendency to buckle or "oil-can" out of the desired uniplanarmode. This is a typical phenomenon in wound composite diaphragms. It istherefore desirable to tailor the fiber orientation of the compositestructure to balance the thermal strain properties of the structure.

Since a fiber wound structure used as a torque drive or a power couplingmust act as a flexure in addition to transferring torque, it is criticalto eliminate or minimize "oil-canning". "Oil-canning" is not desirablefor several reasons. First of all, the torque driving capability of astructure is largely dependent on the stiffness of the structure. Astructure which exhibits "oil-canning" has reduced torsional stiffness.Secondly, the severity of "oil-canning" is a function of temperature.The variations in temperature that a helicopter torque drive or a powercoupling typically encounters (-65° F. to more than 150° F.) will causeundesirable variations in torsional stiffness due to the temperaturefluctuations. Finally, the "oil-canning" or displacement of thediaphragm section results in nonlinear spring characteristics in thetilt mode. This "oil-canning", when the torque drive or coupling isfastened in place, is observed to cause the diaphragm section to buckleand snap-through in a highly nonlinear fashion. This results in dynamicinstability and a potential failure mode of operation. This behavior isunacceptable in a helicopter rotor since it would adversely affect thecontrol characteristics.

The rim reinforcement is incorporated into the torque drive structure ofthe present invention to eliminate the "oil-canning" phenomenon. The rimreinforcement is a circumferential wrap of fiber (tape or roving)applied in a multicircuit pattern until a complete layer or ply of thefiber has been wound. It is preferred to use fibers such as polyaramidor graphite having a negative coefficient of thermal expansion α_(L) forthe rim reinforcement in order to balance the thermal properties of thestructure. The rim reinforcement may be wound before the initial layerof the structure is wound onto the mandrel or after the initial layer orlayers have been wound. The rim circumferential reinforcing wrap isillustrated in FIG. 3, FIG. 5, and FIG. 6. FIG. 5 illustrates athree-circuit retreating pattern wherein the rim is wrapped aroundmandrel 50 with fiber tape 55 in a repeating pattern at approximately120° intervals to produce a circumferential layer and FIG. 6 is afour-circuit retreating pattern wherein the rim is wrapped aroundmandrel 50 with fiber tape 60 in a repeating pattern at approximately90° intervals to produce a circumferential layer. An optional wrap isdemonstrated in FIG. 7 wherein the reinforcing fibers 70 are woundaround mandrel 50 at an angle to and along its radius between thecentral hole and the outer rim; fiber 55 and fiber 65 are shown forcomparison.

It is critical to wind the fibers with sufficient tension to produce the"non-oil-canning" structures of the present invention. Typically thewinding tension will be about 1,000 to about 10,000 pounds per squareinch, preferably about 5,000 pounds per square inch.

The number of structural layers and the number of rim reinforcing layerscontained in any particular torque drive structure will depend upon thesize of the structure, the load, angular velocity and the degree of tiltor articulation during tilt. Preferably more than one structural layeris provided and at least one rim reinforcing layer is provided. The rimreinforcement layers and the structural layers may be wound in any orderor combination. In an example of a particular embodiment, resultant rimreinforcement layers 10 are optionally interleaved with the structurallayers 12 as illustrated in FIG. 3. After the winding is completed,additional fabric reinforcement 11 may be optionally applied to theouter surface of the structure to reinforce the structure for mountingas in FIG. 3.

The fabric will typically comprise woven glass fiber, Kevlar® orgraphite fiber. A preferred fabric is woven Kevlar®49 brand woven clothhaving a thickness of about 0.012". The fabric is preferablypreimpregnated with resin, although the fabric can be impregnated withresin during processing as previously discussed with regard to fibers.

The segmented mandrel wrapped with fiber and resin matrix is then curedin a molding machine under sufficient heat and pressure and for asufficient time period to cure the resin matrix and provide the desiredshape to the structure. Upon cooling, the back portion of the structureis optionally cut out so that a mounting flange remains when used in ahelicopter hub torque drive. When used as a torque drive coupling theback side will not be cut out to form the flange, and both sides of theresulting structure will be identical. The segmented metal mandrel isdisassembled and removed and the rubber covering is pulled out. Thestructure is then drilled around the central hub, hubs, and/or aroundthe flange of the rim or anywhere in the structure to receive fastenersor members. By drilling is meant any material removal process such asdrilling, punching, burning, etc. In addition, the holes may be woundinto the structure by locating projections on the mandrel surface.Typically, the curing cycle used for the structures is a step type cyclein which the temperature is stepped-up at about 2° per minute up to 350°F. The structure is then maintained at 350° F. for about 2 hours andthen cooled off at a rate of 2° per minute to room temperature. It isalso optional to cure at a temperature of about 250° F. The pressureapplied to the part during the cure cycle is typically about 50-300 psi,and preferably about 75 psi. The molding apparatus which can be used tocure and mold the structures of the present invention is typical of heatand pressure molding machines those known in the art and comprises aheated cavity shaped to the surfaces of the structure and a means forapplying pressure.

The fiber to resin ratio of the molded structure after cooling will beabout 55% to about 65% by volume.

The thickness distribution of the wound and molded structure issufficient to provide acceptably uniform stress approximately throughoutthe entire part. Typically, the thickness of the structure is highestnear the central hole, and lower in the diaphragm and higher in the rim.

An embodiment of the torque drive structure of the present invention foruse in a helicopter hub assembly is illustrated in FIG. 1. The structurecomprises a diaphragm section 8 having a rim 2 and an inward turningflange 3. The structure has a central hole therethrough 4 for receivinga shaft. The structure has holes 6 for receiving control rods and holes5 for attaching the structure to a shaft. The structure has holes 7 inflange 3 for attachment.

The structural layer 12 is shown with reinforcing layer 10 and clothreinforcement 11.

The use of the structure as a torque drive diaphragm in the rotor ofrotary wing aircraft such as a helicopter is demonstrated in FIG. 2a andFIG. 2b. Rotor shaft connector 24 is connected to and drives torquedrive diaphragm 21. Torque drive diaphragm 21 is connected by clamp 30to rotor blade 22. Rotor blade 22 has integral with it flex beam 31 andtorque tube 29. Blade pitch is controlled by a push rod 32 acting onpitch arm 33 to turn torque tube 29. Flex beam 31 permits the blade toflex during normal operation of the rotor. Gimbal bearing 23 permits therotor hub to tilt about rotor shaft 24 as a result of various pitchangles applied to the blade 22. Cover 27 protects the rotor and providesan aerodynamic profile. It can be seen from FIG. 2a and 2b that torquedrive diaphragm 21 connects the shaft to the blades thereby drivingtorque to the blades, whereas rotor hub 25 and gimbal bearing 23restrain the blades from centrifugal force and permit the hub to tilt.As rotor hub 23 tilts, torque drive 21 must also tilt. Tilt stop 26controls the maximum degree of tilt.

An embodiment of the present invention for use as a power coupling(e.g., the output shaft of a transmission powering the shaft of amachine, or the output shaft of an electric motor powering a centrifugalpump) is illustrated in FIG. 8 and FIG. 9.

The structure 40 comprises a hollow disc having a first substantiallyflat side 41 and a second parallel substantially flat side 42. Integralrim 43 connects flat side 41 with flat side 42. Flat side 41 has centralhole 43a therethrough for receiving a first shaft. Flat side 42 hascentral hole 44 therethrough for receiving a second shaft. Flat side 41has substantially flat diaphragm section 45 extending from hub section46 to rim 43. Flat side 42 similarly has diaphragm section 47 extendingfrom hub section 48 to rim 43. Hubs sections 46 and 48 optionally haveholes 49 therethrough for attachment.

The structure 40 may optionally have rim 43 longitudinally extended tocomprise a cylindrical or tapered shape. This is accomplished bychanging the shape of the mandrel.

The optional interleaving of the reinforcement fibers with thetangentially wound fibers in the rim section of the structure isillustrated in FIG. 3. Diaphragm or structural layers 12 are seen to beinterleaved with rim reinforcing fibers 10. Optional fabricreinforcement 11 is also illustrated.

The torque drive structures of the present invention will contain holesor voids therethrough for receiving fasteners, control rods, etc. Theholes may be incorporated by conventional methods such as drilling,punching, burning, etc. The holes may also be "wound-in" by havingprojections on the mandrel surface about which the fiber is woundthereby resulting in areas of the structure void of fibers.

The torque drive structures of the present invention have a general usein coupling a high speed, high torque angularly rotating shaft to asecond angularly rotating shaft, member or members, or assembly for thepurpose of powering that shaft or driving the member or members, orassembly. One shaft may have its central longitudinal axis skewed orarticulated up to about 10° with respect to the central longitudinalaxis of the other shaft or assembly. When used as a coupling, ratherthan as a torque drive in a helicopter rotor assembly, the torque drivestructure will be adapted to recieve a shaft on both the front and backsides. The method of manufacture will be similar to that previouslydescribed, except that the back face will not be cut to form a flange,but will be wound and cured to form a hub section with a central holetherethrough for receiving a shaft. So that the structure would beattached on each side to a shaft to function as a flexible torque drivecoupling and each side would have a hub section and a hole therethrough.

EXAMPLE

An approximately one-sixth scale fiber wound torque drive structure foruse in a composite helicopter hub was manufactured by winding Kevlar 29®brand polyaramid fiber around a mandrel. The mandrel comprised an innerdisassemblable segmented metal ring and an outer silicone rubbercoating.

A single layer or ply of Kevlar 29® brand roving was initially woundaround the rim of the mandrel in a 7 circuit retreating pattern to formthe rim reinforcement. Then a single layer or ply of the tape was woundabout the mandrel in an eleven circuit pattern to form the structure.The tape was Kevlar 29® brand polyaramid fiber tape having a thicknessof about 0.006". The tape was about 0.5" wide and comprised nineindividual fiber rovings. The tape was impregnated with an AmericanCyanamid epoxy resin matrix (experimental) no. 1806 having a high straincapacity. The tape was purchased from American Cyanamid Co., Wayne, N.J.The fiber tension during winding was set at about 5,000 pounds persquare inch. Kevlar®29 polyaramid woven fabric was then wrapped aroundthe rim section. The fabric was preimpregnated with the same resinmatrix. The fabric had a thickness of 0.009 inch. The mandrel and woundstructure were placed in a molding machine and the structure was curedby molding at a pressure of about 75 psi with a step-type temperaturecycle wherein the temperature was stepped-up at about 2° per minute toabout 350° F., maintained at 350° F. for about 2 hours, and cooled downat about 2° per minute to room temperature. The structure was drilledaround the central hub and the flange to receive fasteners. The backface of the structure was cut to form a flange and the mandrel andcovering were removed. The structure had a radius of 5.08", and acentral inner hole having a diameter of 1.05". The structure had athickness at the hub of about 0.15" and a thickness at the rim of0.012". The overall depth of the structure was about 0.80".

The structure was mounted in a simulated 1/6 scale helicopter hubassembly test apparatus and rotated at an angular velocity of about1,500 rpm (revolutions per minute) for about 21 million cycles at anglesof up to 8° with no structural failure. No "oil-canning" was observed.

The composite torque drive assemblies of the present invention provide ameans for coupling a rotating drive shaft supplying power at high torqueand high angular velocity to a second driven shaft or assembly whereinthe longitudinal central axis of the shafts, or shaft and assembly, canbe articulated up to about 10° from each other. The torque driveassemblies are constructed of wound synthetic fibers and resin matrix.The multiple angle winding patterns typically used produce predominantlyradial fiber orientation in the peripheral sections of such a structure.The varying temperatures experienced by these structures in a typicalapplication result in differential rates of thermal expansion,particularly at the rim where the epoxy matrix dominates in thetangential direction. The result is an "oil-canning" phenomenon whereinthe normally flat diaphragm takes on a concave or convex shape whenunconstrained. When constrained, the diaphragm buckles, resulting innonlinear spring characteristics and premature failure. It has beenfound according to the present invention that by incorporatingsubstantially tangential reinforcing fibers in the rim, or optionallythroughout the structure, the "oil-canning" phenomenon is eliminated,thereby producing a thermally stable structure which can be used as ahigh torque, high angular velocity, flexible torque drive.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

We claim:
 1. A method of forming a fiber reinforced resin compositestructure, particularly adapted for use as a torque drive diaphragm in arotary wing aircraft hub, comprising winding fiber impregnated withresin on a mandrel with sufficient tension substantially tangentially toa central hole in a multiple circuit pattern to form a diaphragm havinga rim and an inward turning flange, and winding reinforcing fiberimpregnated with resin in an essentially circumferential manner withabout 1000 to about 10,000 pounds per square inch tension to reinforcethe rim of the structure, wherein the reinforcing fibers are interleavedwith the tangential fibers, the structure is then cured by molding atsufficient heat and pressure thereby producing a structure such that thediaphragm remains essentially uniplanar when subjected to stressesinduced by temperature changes.
 2. The method of claim 1 wherein thestructure additionally contains a plurality of holes therethroughradially beyond the outer periphery of the central hole for receivingmembers and fasteners, wherein the holes are either wound into thestructure during the winding process or are created after the moldingprocess, or a combination thereof.
 3. The method of claim 1 wherein aresin impregnated fiber woven fabric is wrapped at least part of thestructure after winding and prior to curing.
 4. The method of claims 1or 3 wherein the fiber is selected from the group consisting of glassfiber, graphite fiber, polyaramid fiber, and a combination thereof. 5.The method of claim 1 wherein the structure is with a fiber tension ofabout 5,000 psi.
 6. The method of claim 1 wherein the diaphragm of thestructure additionally comprises an attachment means centrally locatedabout the central hole.
 7. A method of forming a fiber reinforced resinmatrix composite structure, particularly adapted for use as a flexibletorque drive coupling, comprising winding fiber impregnated with resinon a mandrel substantially tangentially to a central hole withsufficient fiber tension in multiple circuit pattern to form a dischaving a first substantially flat diaphragm side having a central holetherethrough for receiving a shaft and a second substantially flatdiaphragm side having a central hole therethrough for receiving a shaft,said central holes being concentric with the central axis of the disc,said disc having a peripheral rim joining said diaphragm sides and ameans for attachment centrally located around the central holes, andwinding fiber impregnated with resin matrix with about 1000 to about10,000 pounds per square inch tension in a centrally circumferentialmanner to reinforce the rim section of the structure, the reinforcingfibers are interleaved with the tangential fibers, the structure is thencured by molding with sufficient heat and pressure, thereby producing astructure that the diaphragm sides of the structure remain essentiallyuniplanar when subjected to stresses induced by temperature changes. 8.The method of claim 7 wherein an attachment means comprising a hub isformed by molding during the curing process.
 9. The method of claim 7wherein the fibers are selected from the group consisting of glassfiber, graphite fiber, and polyaramid fiber, and a combination thereof.10. The method of claim 7 wherein woven fiber cloth is wrapped about atleast part of the exterior surface of the structure prior to curing. 11.The methods of claim 9 or 10 wherein the fiber is selected from thegroup consisting of glass fiber, graphite fiber, and polyaramid fiberand a combination thereof.
 12. The method of claim 7 wherein thestructure additionally comprises a plurality of holes therethroughradially beyond the outer periphery of the central holes for receivingmembers and fasteners, wherein the holes are either wound into thestructure during the winding process or created after the curingprocess, or a combination thereof.
 13. The structure of claim 7 whereinthe fiber tension is about 5000 psi.
 14. The method of claim 7 whereinthe rim of the structure is extended longitudinally to form a cylinder.15. A method of forming a fiber reinforced resin composite structure,particularly adapted for use as a torque drive diaphragm in a rotarywing aircraft hub, comprising winding fiber impregnated with resin on amandrel with sufficient tension substantially tangentially to a centralhole in a multiple circuit pattern to form a diaphragm having a rim andan inward turning flange, and winding reinforcing fiber impregnated withresin in an essentially circumferential manner with about 1000 to about10,000 pounds per square inch tension to reinforce the rim of thestructure, the structure is then cured by molding at sufficient heat andpressure thereby producing a structure such that the diaphragm remainsessentially uniplanar when subjected to stresses induced by temperaturechanges.
 16. A method of forming a fiber reinforced resin matrixcomposite structure, particularly adapted for use as a flexible torquedrive coupling, comprising winding fiber impregnated with resin on amandrel substantially tangentially to a central hole with sufficientfiber tension in multiple circuit pattern to form a disc having a firstsubstantially flat diaphragm side having a central hole therethrough forreceiving a shaft and a second substantially flat diaphragm side havinga central hole therethrough for receiving a shaft, said central holesbeing concentric with the central axis of the disc, said disc having aperipheral rim joining said diaphragm sides and a means for attachmentcentrally located around the central holes, and winding fiberimpregnated with resin matrix with about 1000 to about 10,000 pounds persquare inch tension in a centrally circumferential manner to reinforcethe rim section of the structure, the structure is then cured by moldingwith sufficient heat and pressure, thereby producing a structure thatthe diaphragm sides of the structure remain essentially uniplanar whensubjected to stresses induced by temperature changes.